Wave guide structure for microwave radio systems



E. DYKE Jan. 11, 1955 WAVE GUIDE STRUCTURE FOR MICROWAVE RADIO SYSTEMSFiled D80. 31, 1949 2 Sheets-Sheet 1 INVENTOR. 122w? ,Dyke BY Jan. 11,1955 WAVE GUIDE STRUCTURE FOR MICROWAVE RADIO SYSTEMS Filed Dec. 51,1949 E. DYKE 2 Sheets-Sheet 2 Jar. J

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United States Patent '0 WAVE GUIDE STRUCTURE FOR MICROWAVE RADIO SYSTEMSEdwin Dyke, Brookfield, Ill., assignor to Motorola, Inc., Chicago, Ill.,a corporation of Illinois Application December 31, 1949, Serial No.136,219

IZ'CIaims. (Cl. 343-180) This invention relates generally to radiocommunication systems and more particularly to a system for providingsimultaneous transmission :and reception at microwave frequencies from asingle antenna.

Radio communication systems for providing dependable .communication overlong distances have been developed which operate at microwavefrequencies. These systems, in most cases, operate on the relayprinciple with a-plurality of intermediate stations being positionedbetween the terminal stations and with the signals being relayed fromone station to another. Although these systems have the advantage thatthey are less expensive than wire lines which provide :the same service,it is desired to further simplify and reduce the cost of such equipmentwhile maintaining the dependability thereof. Since radio signals in themicrowave range are highly directional, it is necessary that theantennas be carefully located so that they will properly directandintercept the microwave beam. In many systems it is desired toprovide continuous communication in both directions with a transmitterat a first station radiating a signal picked up at a second station, anda transmitter at the second station radiatinga signal to be picked up bya receiver at the first station. It is therefore obviously desirable touse a single antenna ateach station for transmission and reception asthis eliminates the cost of one antenna at each terminal station and two.antennas at each relay station, together with the need for carefullyorienting the same and for thereafter maintaining the antennas. Theantennas at the two stations, which are (properly oriented for providingcommunication in one direction therebetween, are, at .the same time,inherently oriented to provide communication in the opposite directiontherebetween. However, many difficulties are encountered in using asingle antenna forboth transmission and reception and a single.antennacan be used only in the event that the strong signal transmittedat each station is prevented from reaching the receiver at that station,and the received signal is not attenuated .by the transmitter so thatreception thereof is interfered with. This difficulty is increased .bythe fact that available oscillator tubes have construction toleranceswhich cause substantial variations in their operating characteristics.

It is therefore an object of the present invention to provide .a simplesystem wherein simultaneous transmission and reception can becarried onwith a single antenna.

Another object is to provide a wave guide structure for use with anantenna for separating waves of different frequencies which are handledby the antenna.

A further object of .this invention is to provide wave guide conductingmeans .including adjustable phase shifting means of simple construction.

A feature of this invention is the provision of a radio communicationsystem includin a plurality of translating devices operating atdifferent frequencies and means coupling the translating devices to asingle antenna so that each device reflects waves of the frequency onwhich the other device operates.

A further feature of this invention is the provision of a microwavecommunication system including an antenna fed by a waveguide and .atransmitter and a receiver coupledto the antenna by branch wave guides,with the wave guide branch connected to the transmitter includingadjustable phase shifting means and. the wave guide branch connected .tothe receiver including a spacer for adjusting-thelength thereof sothatreach branch we ice sents a high impedance to the frequency beingtransmitted through the other branch.

A still further feature of this invention is the provision of a waveguide connected to translating means and forming therewith a reflectingstub, in which the wave guide includes adjustable phase shifting meansfor compensating for variations in the characteristics of thetranslating means.

Further objects and features will be apparent from a consideration ofthe following description when taken in connection with the accompanyingdrawings in which:

Fig. 1 illustrates the communication system in accordance with theinvention;

Fig. 2 is a sectional view through a wave guide illustrating theadjustable phase shifting means;

Fig. 3 is a side view of the structure of Fig. 2;

Fig. 4 illustrates the structure of the cavities formed in a wave guide;and

Fig. 5 illustrates means for adjusting the length of the wave guide.

In practicing the invention there is provided a microwavecommunicationsystem including an antenna having a horn connected to awave guide, and a parabolic reflector for directing the waves emanatingfrom the horn. A flat reflector may be .used for changing the directionof the beam. A transmitter and .a receiver are coupled to the wave guideconnected to the antenna by branch wave guides through a Y junction. Thetransmitter and receiver operate at different frequencies and the branchwave guides connecting them are of such construction that thetransmitting frequency ,is reflected by the receiver branch and thereceiving frequency is reflected by the transmitter branch. To providereflection at the proper frequency, .a spacer is provided in the branchconnected to the receiver which may be changed to provide reflection atthe desired frequency. In the transmitter branch an insulating member isadjustably mounted to shift the phase of the wave passing .therethroughwith the amount of shift depending upon the position of the insulator.The phase shifter is adjustable .to compensate for the use oftransmitting units having different constructions, providing differentreflection characteristics for controlling the overall characteristicsof the transmitting unit and the wave guide branch connected thereto.The phase shifter is Constructed so that the characteristic impedance ofthe wave guide with respect to the transmitter output is substantiallyconstant for all adjustments of the phase shifter. I

Referring now to the drawings, in Fig. 1 there is illustrated acommunication system including a transmitter and receiver unit 10contained ina housing .11. The housing 11 is of such size to receive twotransmitter-receiver units so that a standby or spare .unit can behoused therein. Connected to the transmitter-receiver unit 10 .by waveguide 12 is an antenna assembly including a horn 13, a parabolicreflector 14 and a flat reflector 15. Suitable connecting means 8 may beprovided for alternatively connecting the wave guide 9 to the antennaforconnecting the standby unit thereto. The particular construction ofthe antenna is not essential to the present: inventionand anysatisfactory construction may be used. Connected to' the wave guide 12is a Y junction including a wave guide portion 16 connected to the waveguide 12 and branch wave guides 17 and 18 connected to the receiver 19and the transmitter 20 respectively. The wave guide 17 is connected tothe receiver 19 through a spacer 21 which may be changed as will bedescribed more in detail.

The receiver 19 includes a triple cavity composed of sections 22, 23 and24 at the input portions thereof. As shown more in detail in Fig. 4,adjusting screws 25 are provided for adjusting the volume of thesections of the cavity so that the frequency response thereof can becontrolled. This cavity has a relatively high Q so that the frequency tobe received is passed thereby but other frequencies outside the band tobe received are very sharply attenuated. A Q of the order of 350 persection has been found highly satisfactory for such a triple cavityfilter. The waves which pass through the filter continue to'the mixingportion 26 where they are gplmbined with local oscillations produced byan oscillator 7 made to Figs. 2 and 3.

The oscillator 27 may be any suitable high frequency oscillator such asa klystron or a magnetron. An adjustable attenuating device 28 isprovided for controlling the amplitude of the oscillations from thelocal oscillator. The wave from the local oscillator passes along thewave guide portion 29 with a part of the waves going throu h thedirectional coupler 31) into the mixing portion 26. The directionalcoupler includes a pair of openings separated by a barrier, and iseffective to allow the local oscillations to enter the mixing portionbut prevent the received wave from entering the wave guide portion 29.The mixing is accomplished by crystal unit 31 which is connected to anintermediate frequency amplifier, not shown. An adjustableplunger 32 isprovided in the mixmg portion so that this portion can be properly tunedto compensate for variations in individual crystal mixers.

The wave guide portion 29 also includes monitoring provisions includinga cavity 33 with an ad usting screw which passes the frequency of thelocal oscillator. and a crystal 34 coupled to suitable indicating orcontrol means which will indicate to the operator that the oscillator isproperly adjusted. A motor 35 is provided and is coupled throu h a driverod 36 to the oscillator 27 for changing the frequency of theoscillator. The motor 35 can be remotely controlled so that the operatorcan intake any necessary changes in the frequency of the oscila or.

As previously stated the wave guide branch 18 is connected to atransmitter 20. This transmitter includes a modulated oscillator whichmay preferably be an oscillator of the type that can be directly orinternally modulated such as a klystron or a magnetron. In the waveguide branch 18 there is provided phase shifting means 40 wh1c h maytake the form of a polystyrene member extending along the path of thewave guide. An adiustable mounting 41 is provided for the phase sh ftingmember 4Q for adiustably supporting the phase shifting member within theguide. The amount of phase shift produced by the member 40 depends uponthe position thereof within the guide, as will be more fully ex lained.Cou led to the wave guide 18 is a wave guide 42 which includesprovisions for monitoring the transmitter. A cavity 43 selects thetransmitter frequency and a crystal 44 is connected to suitableindicating or control means at the central station for indicating thefrequency of the transmitter to the o erator. Such indicating means mayshow a maximum indication when the transmitter frequency corresponds tothe resonant frequency of the cavity. A wave absorbin member 45 isprovided at the other end of the wave uide 42 to absorb waves in this prtion of the wave guide. The wave absorbing member 45 may be made of anymaterial capable of absorbing waves of the freouencies involved such asa material formed of iron articles separated by insulating material andknown as Polyiron. A motor 6 is cou led to the transmitter 20 throughcontrol rod 47 for remotely controllin the oscillator in the same manneras previously described with respect to the local oscillator 27. An adustable plunger 48 is provided for tunin the wave guide section to whichthe oscillator is coupled.

For a more complete consi eration of the construction and operation ofthe phase shifting means 40, reference is The hase shifting meansincludes an insulating member 49 having slanting ends 5i) which may beoffset as shown. The mounting means includes a block 51 secured in ahousing 52 extending from the wave guide 18. The block includes opening53 for guide rods 54 and an opening 55 for a rack 56. In one method ofassembly the guide rods 54 and the rack 56 may be secured to theinsulating member 49 for supporting the same. The teeth on the rack 56engage teeth on pinion 57 which is provided in a transverse opening inthe block 51. A screwdriver slot 58 may be provided in one end of thepinion 57 which is accessible through an opening 59 in the housing 52 sothat the pinion may be turned to adjust the position of the phaseshifting member. The insulating member 49 should be made of a materialhaving a relatively high dielectric constant and relatively low losses.Polystyrene has been found to be very suitable for this purpose. Theinsulating member must be shaped so that the standing wave ratio in theguide observed from the transmitter end is substantially the same forall positions of the phase shifting means so that the impedance of theguide will remain 4 substantially constant. This may be provided by theoffset and slanting ends of the insulating member as illustrated and byproperly spacing the rack 56 and guide rods 54. In the structuredisclosed, it is possible to produce phase shifts of the waves amountingto more than 180 degrees by changing the position of the member 49.However, such a wide variation may not be necessary to compensate forthe differences in the construction of the trans-' mitting tubes andphase shifting means providing smaller variations may be suitable insome cases.

In Figs. 2 and 3 there is also illustrated more in detail theconfiguration of the wave absorbing member 45. This member is of astepped configuration with a base portion 60 having shoulders 61 bearingagainst the end of the guide 42 and an intermediate portion 62 whichfits snugly within the end of the guide. An end 63 of reducedcross-section extends within the guide in such manner to be engaged bywaves in this portion of the transmitter monitoring section.

In Fig. 5 there is illustrated the configuration of the adjustableplungers such as identified at 32 and 48 in Fig. 1. These plungersinclude movable plates hav ing edges 71 shaped to make sliding contactalong the inner surface of the wave guide. The plate 70 is secured to arack 72 having teeth engaging the teeth of pinion 73. Therack 72 andpinion 73 may be identical to the rack 56 and pinion 57 of Fig. 2. Thepinion 73 may also include a slot to be engaged by a screwdriver foradjusting the position of the plate 70.

The attenuating member 28 of Fig. 1 may be mounted in the same manner asthe phase shifting means 40 as illustrated in Fig. 2. The attenuatingmember has a high resistance to the wave and may be constructed ofinsulating material such as Bakelite with a very thin film of conductingmaterial on one side thereof. Such a conducting film may be made of acarbon or platinum in a very thin film to provide a high resistance.

Considering now the operation of the system, the oscillator 20 producesa wave which is transmitted through wave guide branch 18 to the Yjunction and through the wave guide 12 to the horn 13 of the antenna.The wave is reflected and beamed by the parabolic reflector 14 and thedirection of the beam then changed by the flat reflector 15. The wavefrom the transmitter would also tend to be directed through the branchwave guide portion 17 to the receiver which is, in effect, in parallelto the wave guide 12. However, the length of the guide 17 and the spacer21, and the portion of the guide in the receiver ahead of the iris 38 ofthe first cavity 22, are of such length that a high impedance ispresented to waves of the frequency of the transmitter 20. This has thedesirable effect of eliminating waves of this frequency from thereceiver and also eliminating the attenuation of the transmitted wavewhich would be caused by the parallel path through which a portion ofthe transmitted wave might be diverted. The high impedance of thereceiver branch at the transmitting frequencies also eliminatesattenuation due to an impedance mismatch at the Y junction which mightotherwise occur. When it is desired to change transmitting frequencies,a spacer 21 of a different length can be provided so that the system maybe easily converted for operation on different frequencies.

The received waves, which are of different frequency than thetransmitted waves, are picked up by the from 13 and pass through waveguide 12 and through the Y junction and branch guide 17 to the receiver19. The received frequencies are passed by the triple cavity filter andmixed with local oscillations as previously described. The branch guide18 from the Y junction to the transmitter is of such length that itpresents a high impedance at the received frequency and therefore thisfrequency will not be attenuated by the transmitter branch but will beapplied entirely to the receiver. The effective length of the wave guide18 is adjusted by the phase shifting member 40. The phase shiftingmember 40 therefore serves an analogous function to the spacer 21 inthat the receiving frequency can be changed and the phase shifter can beadjusted to change the angle at which waves are reflected by the waveguide 18 so that the wave guide pre sents a high impedance to the newreceived frequency.

The phase shifter 41) however has an additional function which is tocompensate for different oscillators used in the transmitter. It hasbeen found that various ldystrons and magnetronsavailable have slightlydifferent con:

" structions which impart different reflection characteristics thereto.One reason for this is that tubes such as these may include a shortsection of transmission line and slight variations in length produceappreciable changes in characteristics. The length of the wave guide 18therefore has to be particularly adjusted for the different oscillatorsused. This is obviously undesirable and therefore the phase shifter 40which is easily adjustable solves a very diificult problem in systems ofthis type. The settings of the pinion 57 may be adjusted each time theoscillator tube is changed and/or each time the receiving frequency ischanged, thereby controlling the effective length of the wave guide 18so that the reflection of the received wave by the transmitter portionof the system does not substantially attenuate the received wave.

The above system has been found to be highly satisfactory and providessimultaneous transmission and reception from a single antenna withoutobjectionable interference. The system is adaptable for use withtransmitters and receivers operating at different frequencies within thesame range of frequencies and the frequencies of operation can bechanged without substantial changes in the equipment. The simpleadjustment of the phase shifter in the transmitter branch of the waveguide permits easy adjustment to compensate for changes in oscillatortubes. A similar arrangement can be used in the receiver but since thelength from the junction to the first iris of the cavity in the receivermay be accurately determined, it is easy to compute the size of spacerrequired for each frequency and a spacer as illustrated is entirelysatisfactory. In most systerms the frequencies of operation will not besubject to change.

It is to be pointed out that other devices may be used for changing thecharacteristics of the wave guides for controlling the impedancethereof, but the ones described have been found to be the most simpleand effective for the particular application set forth.

Although one embodiment of the invention which is illustrative thereofis disclosed, it is obvious that various changes and modifications canbe made therein without departing from the intended scope of theinvention as defined in the appended claims.

I claim:

1. A system for providing simultaneous operation of a plurality ofmicrowave translating units from a single antenna comprising, antennameans, a first translating unit operating at a first frequency, firstWave guide means coupling said first unit to said antenna means, asecond translating unit operating at a second frequency, and second waveguide means coupling said second unit to said antenna means, said firsttranslating unit including an electron discharge valve of suchconstruction that the reflection characteristics thereof varysubstantially with slight changes in the dimensions thereof, said firstwave guide means including a tubular duct, an insulating memberpositioned therein, and adjustable means for supporting said insulatingmember in various positions with respect to said tubular duct, saidinsulating member being so constructed and arranged that the phase ofwaves passing through said first wave guide means is shifted by anamount depending on the position of said insulating member and that saidfirst wave guide means presents a substantially constant impedance tosaid first translating unit for all positions of said insulating member,whereby said elongated member compensates for variations in thereflection characteristics of said valve of said transmitter to presenta high impedance to waves of said second frequency.

2. A system for providing simultaneous microwave transmission andreception from a single antenna comprising, antenna means, a transmitteroperating at a first frequency, first Wave guide means coupling saidtransmitter to said antenna means, a receiver operating at a secondfrequency, and second wave guide means coupling said receiver to saidantenna means, said transmitter including an electron discharge valve ofsuch construction that the reflection characteristics thereof varysubstantially with slight changes in the dimensions thereof, said firstwave guide means including a tubular duct, a polystyrene member ofelongated shape and having tapered ends positioned longitudinally withinsaid duct, and adjustable means for supporting said elongated member invarious positions with respect to a side wall of said tubular duct, saidpolystyrene member being positioned to shift the phase of waves passingthrough said duct by an amount such that waves of said second frequencyare reflected by said first wave guide means and said transmitter incombination,

said first wave guide means presenting a substantially constantimpedance to said transmitter for all positions of said polystyrenemember, said second wave guide means and said receiver having suchdimensions to reflect waves of said first frequency.

3. A system for providing simultaneous microwave transmission andreception from a single antenna comprising, antenna means, wave guidemeans including a main portion coupled to said antenna means and firstand second branch portions connected to said main portion, transmittermeans coupled to said first branch portion for transmitting waves of afirst frequency, receiver means coupled to said second branch portionfor receiving waves of a second frequency, said receiving meansincluding wave guide structure having first, second, third, and fourthinterconnected sections, said first section being connected to saidsecond branch portion and cooperating therewith to reflect waves of saidfirst frequency, said second section including a resonant cavity filterwhich passes waves of said frequency, said fourth section includingmeans for generating waves having a frequency differing from said secondfrequency by a predetermined frequency, said third section being coupledintermediate said second and fourth sections and mixing the wavesprovided thereby to provide waves having said predetermined frequency,said transmitter means including a wave guide section and an electrondischarge valve coupled thereto, the reflection characteristics of saidtransmitter means depending upon the particular construction of saidvalve, and adjustable phase shifting means coupled to said first branchportion for controlling the over-all reflection characteristics of saidfirst branch portion and said transmitter means so that a high impedanceis presented to waves of said second frequency.

4. A system for providing simultaneous microwave transmission andreception from a single antenna comprising, antenna means, Wave guidemeans including a main portion coupled to said antenna means and firstand second branch portions connected to said main portion, transmittermeans coupled to said first branch portion for transmitting Waves of afirst frequency, receiver means coupled to said second branch portionfor receiving waves of a second frequency, said receiving meansincluding a Wave guide structure having first, second, third, and fourthinterconnected sections, said first section being connected to saidsecond branch portion and cooperating therewith to present a high in!-pedance to waves of said first frequency, said second section includinga resonant cavity filter which passes waves of said second frequency,said fourth section including means for generating waves having afrequency differing from said second frequency by a predeterminedfrequency, said third section being coupled intermediate said second andfourth sections for mixing the waves provided thereby to provide waveshaving said predetermined frequency, means for adjusting the effectivelength of said third section for tuning the same to said predeterminedfrequency, said transmitter means including a waveguide section and anelectron discharge valve coupled thereto, means for adjusting the lengthof said wave guide section of said transmitter means for tuning the sameto said second frequency, the reflection characteristics of saidtransmitter means depending upon the particular construction of saidvalve, and adjustable phase shifting means coupled to said first branchportion for controlling the combined reflection characteristics of saidfirst branch portion and said transmitter to present a high impedance towaves of said second frequency.

5. A system for providing simultaneous microwave transmission andreception from a single antenna comprising, antenna means, wave guidemeans and first and second branch portions connected to said main portion, transmitter means coupled to said first branch portion fortransmitting waves of a first frequency, receiver means coupled to saidsecond branch portion for receiving waves of a second frequency, saidreceiving means including wave guide structure having first, second,third, and fourth interconnected sections, said first section beingconnected to said second branch portion and cooperating therewith topresent a high impedance to waves of said first frequency, said secondsection including a resonant cavity filter which passes waves of saidsecond frequency, said fourth section including means for generatingwaves having a frequency difiering from :said second frequency by :apredetermined frequency, monitoring means rfor :said wave gen- ;erating=means-coupled to said fourth section, said third :section being coupledintermediate said second and fourth sections and mixing the wavesprovided thereby to provide waves having said predetermined frequency,said transmitter means including a wave guide section and an electrondischarge valve coupled thereto, the treflection characteristics of saidtransmitter means depending =upon the particular construction of saidvalve, adjustable phase shifting means coupled to said first tbranchportion for controlling the over-all reflection characteristics'of saidfirst branch portion and said transmitter means to present a highimpedance to waves of said second frequency, and monitoring means forsaid transmitter coupled to said first branch portion.

6. A system for providing simultaneous microwave transmission andreception from a single antenna comprising, antenna means, wave guidemeans and first andsecond branch portions connected to said main por-;tion, transmitter means coupled to said first branch portion fortransmitting waves of a first frequency, receiver means coupled to saidsecond branch portion for receiving waves of a second frequency, saidreceiving means including wave guide structure having first, second,third, and fourth interconnected sections, said first section beingconnected to said second branch portion and including a spacer havingsuch length that a high impedance is presented to waves of said firstfrequency, said second section including a resonant cavity filter whichpasses waves of said second frequency, said fourth section includingmeans for generating waves having a frequency differing from said secondfrequency by a predetermined frequency, said thirdsec tion being coupledintermediate said second and fourth sections and mixing the wavesprovided thereby to provide waves having said predetermined frequency,said transmitter means including a wave guide section and an electrondischarge valve coupled thereto, the reflection characteristics of saidtransmitter means depending upon the particular construction of saidvalve, and adjustable phase shifting means coupled to said first branchportion for controlling the over-all reflection characteristics ofsaidtfirst branch portion and said transmitter means so that a highimpedance is presented thereby to waves of said second frequency, saidphase shifting means including an elongated insulating member extendinglongitudinally within said first branch portion and means for adjustablypositioning said insulating member with respect to the walls of saidfirst branch portion.

7; A communication system including in combination, a transmitteroperating at a first frequency, a receiver operating at a secondfrequency, an antenna, and wave guide means coupling said transmitterand said receiver to said antenna for simultaneous operation therewith,said wave guide means including a main portionand first and secondbranch portions extending from said main portion, said main portionbeing connected to said antenna and said first and second branchportions being individually connected respectively to said transmitterand said receiver, said transmitter including wave guide means connectedto said first branch portion and having a wave reflecting portion thechar- .teristics of which vary with slight changes in the dimensionsthereof, said first branch portion including phase shifting meansadjustable to change the effective length thereof, said phase shiftingmeans being adjusted so that said first wave guide branch portion andsaid transmitter wave guide means together form a stub of such effectivelength that waves of said second frequency are reflected thereby withoutsubstantial attenuation, said receiver including a wave guide portionconnected to said second branch portion and including high Q band-passresonant cavity means for selecting waves of said second frequency withsaid cavity means having an iris at the input thereof, said secondbranch portion having such length that this portion together with thepart of said receiver wave guide portion up to said iris form a stub ofsuch effective length that waves of said second frequency are reflectedthereby without substantial attenuation, whereby said transmitter andsaid receiver are both efliciently coupled to said antenna forsimultaneous operation therewith.

"8. A communication system including in combination, a first translatingunit operating at a first fre- 8 'quency, 'a se'con'd translating 'unitoperating :at a second frequency, an antenna, and wave 'guide' tn'eansfor simul- 'taneously coupling Jsaid tfirst and second translating units;to .said antenna, said wave guide means including a main portion andfirst and second branch portions "extending from .said main portion,said main portion be- 'ing connected to said antenna and said first andsecond branch portions being individually connected respectively to saidtranslating units, said first translating unit including wave guidemeans connected to :said first branch portion and having a wavereflecting portion the characteristics of which vary with slight changesin the dimensions thereof, said first branch portion including phaseshifting means adjustable to change the effective length thereof, saidphase shifting means being adjusted so that said first wave guide branchportion and said wave guide means of said first unit together form astub of such effective length to present a high impedance to waves ofsaid second frequency, said second translating unit including a waveguide portion connected to said second branch portion and bandpassresonant cavity :means for selecting waves of said second frequency,said cavity means having an iris at the input thereof connected to saidwave guide portion of said second unit, said second branch portionhaving such length that this portion together with said 'wave guideportion of said second unit form a stub of such effective length topresent a high impedance to waves of said second frequency, whereby saidfirst and second translating units are both efficiently coupled to saidantenna for simultaneous operation therewith.

9. Microwave radio apparatus including in combination, a transmitteropera-ting at a first frequency, a receiver operating at a secondfrequency, an antenna for operation with said transmitter and receiverand having a hollow wave guide portion for coupling signals thereto,said transmitter having a hollow waveguide portionconnected to said waveguide portion of said antenna, said receiver having a hollow wave guideportion connected to the junction of said wave guide portions of saidtransmitter and said antenna, said transmitter including an electrondischarge valve having reflection characteristics which may differ witheach particular valve, said wave guide portion of said transmitterincluding adjustable phase shifting means therein, said phase shiftingmeans being adjusted to compensate for the reflection characteristicsofsaid valve so that said transmitter and said wave guide portion thereofform a stub of such efiective length to present a high impedance towaves of said second frequency, said wave guide portion of said receiverhaving therein tuned filter means constructed to select said secondfrequency and reject said first frequency, said filter means including aplurality of irises which define a plurality of high Q cavity filtersections, said iris of said filter means nearest said antenna being sopositioned with respect to said wave guide portions of said antenna andsaidtransmitter to present a high impedance to waves-of said firstfrequency applied from said transmitter to said antenna.

10. A system for providing simultaneous microwave transmission andreception from a single antenna includingin combination, antenna means,tra-nsmitter'means for transmitting waves of a first frequency, hollowwave-guide means interconnecting said transmitter means and said antennameans, receiver means coupled to said wave guide means for receivingwaves to a second frequency, said receiver means including a hollow waveguide structure having firs-t, second and third interconnected sections,said first section having therein a resonant cavity filter tuned toselect waves of said second frequency, said resonant cavity filter beingpositioned with respect to said wave guide means to reflect waves ofsaid first frequency passing through said waveguide means from saidtransmitter means to said antenna means without substantiallyattenuating -the same, said third section including means for generatingwaves having a frequency differing from said second frequency by apredetermined frequency, said second section being coupled intermediatesaid first and third sections and mixing the waves provided thereby toproduce waves having said predetermined frequency, said transmittermeans including a Waveguide section and an electron discharge valvecoupled thereto, said transmitter means having reflectioncharacteristics, and adjustable phase shifting means in theportion ofsaid wave guide means intermediate said receiver means and transmittermeans, said phase shifting means controlling the overall reflectioncharacteristics of said portion of said Wave guide means and saidtransmitter means so that a high impedance is presented thereby to wavesof said second frequency.

11. Microwave radio apparatus including in combination, 'a transmitteroperating at a first frequency, a receiver operating at a secondfrequency, an antenna for operation with said transmitter and receiverand having a hollow wave guide portion for coupling signals thereto,said transmitter having a hollow wave guide portion connected to saidwave guide portion of said antenna, said receiver having a hollow waveguide portion connected to the junction of said wave guide portions ofsaid transmitter and said antenna, said wave guide portion of saidtransmitter including adjustable phase shifting means, said phaseshifting means being adjusted so that said transmitter and said waveguide portion thereof form a stub of such effective length that waves ofsaid second frequency are reflected thereby, so that waves of saidsecond frequency received by said antenna are applied therefrom to saidreceiver without substantial attenuation, said wave guide portion ofsaid receiver including tuned filter means constructed to select saidsecond frequency and reject said first frequency, said filter meansincluding a plurality of irises which define a plurality of high Qcavity filter sections, said iris of said cavity means nearest saidantenna being positioned with respect to wave guide portions of saidantenna and said transmitter that waves of said first frequency appliedfrom said transmitter to said antenna are reflected thereby, so thatwaves of said first frequency from said transmitter are applied to saidantenna without substantial attenuation.

12. A compact microwave unit for providing simultaneous microwavetransmission and reception from a single antenna including incombination, antenna means, transmitter means for transmitting waves ofa first frequency and including an electron discharge valve, hollowsingle conductor wave guide means interconnecting said transmitter meansand said antenna means, receiver means for receiving waves of a secondfrequency coupled to said wave guide means at an intersection thereonintermediate said transmitter means and said antenna means, the portionof said wave guide means extending between said intersection and saidtransmitter means together with said transmitter means forming a stub ofsuch effective length to present a high impedance to waves of saidsecond frequency, said receiver means including rigid wave guidestructure having first, second and third interconnected sections, saidfirst section having therein a resonant cavity filter tuned to selectwaves of said second frequency, said resonant cavity filter beingpositioned with respect to said wave guide means to reflect waves ofsaid first frequency passing through said wave guide means from saidtransmitter means to said antenna means without substantiallyattenuating the same, said third section extending substantiallyparallel to said first section and including means for generating Waveshaving a frequency differing from said second frequency by apredetermined frequency, said second section being coupled intermediatesaid first and third sections and mixing the waves provided thereby toproduce waves having said predetermined frequency, said portion of saidwave guide means extending between said intersection and saidtransmitter means having a substantial part thereof extendingsubstantially parallel to said first section of said wave guidestructure of said receiver means, so that said transmitter means andsaid receiver means together form a compact unit.

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